1. Field of the Invention
The present invention relates to a current sensor configured to measure a target current to be measured, in a non-contact manner.
2. Description of the Related Art
In a field such as motor drive technologies for electric cars and hybrid cars, a relatively large current is used. Thus, a current sensor capable of measuring large current in a non-contact manner is sought for such a use. As such a current sensor, a sensor using a method in which a change in magnetic field is detected by a magnetic sensor has been proposed, the change being caused by a target current to be measured. For example, Japanese Unexamined Patent Application Publication No. 2002-156390 discloses a current sensor in which a magnetic resistance element is used as an element for a magnetic sensor.
For the above-described current sensor, which is a non-contact type current sensor, current-detection performance may be degraded due to deterioration of an element with age. Thus, in a field whose top priority is to ensure safety, such as in a field regarding devices mounted in vehicles, it may be necessary to determine whether a malfunction has occurred or not in the current sensor in order to realize a fail safe design. As a method for determining whether a malfunction has occurred or not in the current sensor, Japanese Unexamined Patent Application Publication No. 2003-194598 discloses a malfunction detection method in which determination is performed in accordance with whether the sum of output values from two sensors (an addition value of output values) is constant or not.
However, an addition value of output value used to perform malfunction determination in Japanese Unexamined Patent Application Publication No. 2003-194598 changes under the influence of an adscititious magnetic field (the earth's magnetic field, an induction field generated by current that flows through an adjacent wire, or the like). Thus, in the case where, for example, the influence due to a malfunction is almost at the same level as or is smaller than the influence due to an adscititious magnetic field, the influence due to the malfunction is masked by the influence due to the adscititious magnetic field. Consequently, malfunction determination is not properly performed.